The invention relates to improvements in components of power trains in motor vehicles, such as clutch plates in friction clutches or similar aggregates or systems which transmit torque between the engine and the variable-speed transmission of an automobile, truck or another engine-driven conveyance. More particularly, the invention relates to improvements in components of the type wherein a carrier of friction linings can be caused to transmit torque to a hub (and vice versa), and the carrier and hub can turn relative to each other in at least one direction against the opposition of several energy storing units including a first or primary unit which can oppose angular movements of the carrier and the hub relative to each other independently of the other unit or units while the carrier moves away from a starting or neutral position with reference to the hub or vice versa.
In accordance with a presently known proposal, the energy storing elements of the primary unit are caused to store energy during idling of the engine but are bypassed as the RPM of the engine increases beyond the idling speed. For example, the energy storing elements of the primary energy storing unit can be bypassed by blocking or locking members which are acted upon by centrifugal force and become effective when the RPM rises above the idling speed. This is believed to enhance the damping ability and the ability of the power train to counteract the fluctuations of load, especially to suppress vibrations which develop when the engine is operated under load. Since the space under the hood and elsewhere in a motor vehicle is at a premium, the aforediscussed means for bypassing the idling damper or dampers must necessarily rely on compact blocking or locking members whose mass is small so that such members are incapable of reacting with the required degree of reliability when the centrifugal force increases or decreases, especially when the RPM of the engine is relatively low. This creates problems because such compact members are apt to bypass the primary damper or dampers at an inopportune time or to fail to deactivate or sideline the primary damper or dampers when the action of such damper or dampers is unnecessary or undesirable. Furthermore, the accuracy of blocking or bypassing devices which rely on centrifugal force is insufficient on the additional ground that frictional hysteresis develops between the moving parts. Such hysteresis opposes the blocking or locking action of blocking members which are influenced by centrifugal force when the RPM of the engine increases, and it opposes the unblocking of the primary damper or dampers when the RPM of the engine decreases. All in all, it is not possible to select the exact RPM for the activation or bypassing of the primary damper or dampers with a degree of predictability which is desirable and necessary in the power train of a motor vehicle. Therefore, the primary damper or dampers are blocked or bypassed at a speed which is well above the idling RPM.